Patent Publication 1 describes a well-known method of friction welding for bonding a pair of works. This method consists of relatively rotating the pair of the works while the end surfaces of the works are in contact with each other to generate friction heat on the end surfaces, and then applying an upset pressure for producing an interatomic attraction for integrating the pair of the works. This method eliminates the necessities of supplying a heat source other than the friction heat and of the use of a welding rod and flux.
Generally, in this method, before a first work gets in contact with a second work, the second work is moved (fast forwarded) from a specified moving start position toward the first work for a specified distance (fast forwarding distance) while the first work is rotated under fixation. Then, for achieving the contact between the pair of the works without the damages of the works and a processing machine, the second work is moved (slowly forwarded) toward the first work at a forwarding speed (hereinafter referred to as “slowly forwarding speed”) slower than the forwarding speed during the fast forwarding (hereinafter referred to as “fast forwarding speed”), thereby contacting the second work to the first work.
A dimension error possibly existing in the work generates a threat that the send work impacts the first work not during the slow forwarding but during the fast forwarding. In order to avoid this occurrence, the slowly forwarding distance is set longer when the work dimension is legitimate in consideration that the work dimension is made longer than the legitimate dimension due to the dimension error under the assumption of the second work is fast forwarded from the specified moving start position toward the first work for the specified distance (fast forwarding distance) (The slowly forwarding distance is set as the total of “anticipated maximum dimension error when it is made longer than the legitimate dimensions for both of the works”+“a moving distance at the slowly forwarding speed in the above case”) (refer and compare a first case when the dimension is legitimate with a second case when the dimension is longer than the legitimate in FIG. 4).